The invention relates to polyol formulations based on aromatic aminopolyols and to the flame-resistant rigid foams produced therefrom.
Isocyanate-based foams are widely used for the insulation of buildings, parts of buildings, pipes, containers and many other things against the loss of coldness or heat, and also for the reinforcement of components. It should be remembered that insulating materials of this type must have specific properties when exposed to a flame, particularly when they are used in the construction industry. These properties vary from country to country. In the Federal Republic of Germany, the flame propagation characteristic determined in accordance with DIN 4102 is crucial. To achieve particularly good insulating effect, chlorofluorocarbons and chlorofluorohydrocarbons are still widely used as physical blowing agents. However, it has been found that these materials can probably represent a considerable risk for the essential atmospheric ozone layer. A challenge for industrial progress is to provide foams in which these materials are no longer necessary.
One method which is already being widely adopted is the exclusive use of water as a blowing agent. The fact that the carbon dioxide formed from water and isocyanates and acting as a blowing agent leaves the foam cells more quickly than air enters those cells subjects the foam to considerable stress. This necessitates increased pressure resistance and therefore usually undesirably increased densities in the foam. The use of other chemical blowing agents such a carbamates or carboxylic acids has the same drawback. The use of formic acid or formates can also lead to the emission of toxic carbon monoxide.
Fluorinated hydrocarbons are alternative blowing agents. R134a is widely used and, due to its gaseous state at ambient temperature and its low solubility in the conventional components used to produce isocyanate-based foams, leads to considerable handling problems and to a minimal improvement over purely water-blown foams. Other fluorinated hydrocarbons are characterized by sometimes expensive production processes. Mixtures of these blowing agents with polyols can have a flashpoint below 55° C. so they can be handled only after taking safety precautions.
The use of tert.butanol for the production of integral-skin foams with a solid outer skin is known. Tert.butanol as a blowing agent has the drawback that the reaction temperature required to release the blowing agent is not attained or is attained too late in outer regions and on cold surfaces and the low density desired for the insulating effect cannot be obtained. This is particularly important in outdoor applications where the foam is applied to the often cold and unheatable component to be insulated. Tert.butanol is also flammable at low temperatures; furthermore, the addition of tert.butanol can lead to a polyol flash point below 55° C.
Due to their favorable cost, alkanes are widely used as blowing agents. These products also have the drawback of flammability which, on the one hand, necessitates safety precautions in processing and, on the other hand, leads to less desirable behavior in various standardized flammability tests. This can be compensated for, in part, by addition of relatively large quantities of flame retardants to the foams. Frequently, however, this adversely affects other properties of the foam.
BE-A 680691 discloses the use of Mannich bases in conjunction with chlorinated, ozone-destroying blowing agents and without the use of polyester polyols for the production of polyurethane rigid foams. In that case, however, it is preferable to use alkoxylated Mannich bases as raw materials for the production of such foams. The use of alkoxylated Mannich bases in conjunction with polyester polyols and ozone-depleting blowing agents is known, for example, from U.S. Pat. No. 5,451,615. However, alkoxylated Mannich bases are more expensive to produce due to the additional required step of alkoxylation. U.S. Pat. No. 4,489,178 discloses the production of rigid polyurethane foams with improved flame retardance whereby alkoxylated Mannich bases form the polyol component.
EP-B 0 854 159 discloses a process for the production of rigid polyurethane foams which develop little smoke in case of fire.